The point of having a max effective health set is that you don't care about avoidance, its about surviving a big hit so healers have a chance to get you up. That being said, your effective health gear is not necessarily supposed to be the set for the hardest bosses, just ones where you don't have enough EH to survive otherwise. Kael, you need giant amounts of hp, a low avoidance doesn't factor in, you need to be able to eat some 23 k pyros.
For instance, with the avoidance values you have so far, yeah, I would say that's going to cause problems on many bosses, because at that rate of avoidance, bosses will be eating up SB charges very frequently, leaving you open to crushes. However, if this EH set of yours gives you the minimum requirement to survive the boss assuming the heals come in, you don't have much of a choice.
I tanked through all of SSC/TK with 15% dodge & 15% parry with a little over 490 defense. The only boss I would have wanted more avoidance for was Al'ar. Once you hit BT/Hyjal it starts favoring 20+ dodge with 18%+ parry though. So unless you're doing T6 content, yes, 15% dodge/15% parry is just fine.